In a recent wiring technology, copper lines are replacing aluminum lines to improve performance of a semiconductor device. In a manufacturing process of the semiconductor device, a technology for forming a copper film on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) is important. A chemical vapor deposition method (hereinafter, referred to as “CVD”) using a copper organic compound as a material has been known as one of technologies for forming a copper film on the wafer.
When a copper film is formed on the wafer by using CVD, a copper organic compound, e.g., Cu(hexafluoroacetylacetonate) trimethylvinylsilane (hereinafter, referred to as “Cu(hfac)TMVS”) serving as a source gas is supplied to a processing chamber in a vacuum state, and the Cu(hfac)TMVS is thermally decomposed on the heated wafer to form the copper film on the surface of the wafer. However, since copper atoms tend to be diffused into the wafer, in most cases, the copper film is formed on a diffusion barrier film (base film) called a barrier metal, which is formed in advance on the wafer, instead of being directly formed on the wafer. The base film employs titanium, tantalum or nitride thereof. When the base film is made of a metal having a high oxidation tendency, an organic impurity layer is formed between the base film and the copper film.
When the organic impurity layer is interposed between the base film and the copper film, adhesiveness between the base film and the copper film is weakened and a resistance between an upper copper line and a lower copper line increases. Accordingly, electrical characteristics deteriorate or the copper film is peeled off while processing the wafer, resulting in a reduction in production yield. Further, since the organic impurity layer has poorer wettability than the base film, copper can be easily aggregated to thereby reduce buriability of the copper in a trench having a high aspect ratio, thereby causing a defect of the copper line.
In order to solve the above-mentioned problem of formation of the organic impurity layer, Patent Document 1 discloses a technique using water vapor. In accordance with the technique disclosed in Patent Document 1, CVD is performed after water vapor is supplied to a processing chamber containing a wafer, thereby preventing formation of an organic impurity layer.
However, in the CVD using Cu(hfac)TMVS as a material, the water vapor oxidizes a surface of the base film made of a metal having a high oxidation tendency (that is, easily oxidized) to thereby form an oxide layer between the base film and the copper film though it prevents formation of the organic impurity layer. The oxide layer decreases adhesiveness between the base film and the copper film. Accordingly, although the formation of the organic impurity layer is prevented, it is difficult to improve adhesiveness between the copper film and the base film.
Further, according to the investigation of the inventors, when the CVD using Cu(hfac)TMVS as a material is performed in an atmosphere containing water vapor, it is possible to reduce a film forming temperature (wafer temperature) of the copper film. As known in the art, the reduction of the film forming temperature can improve morphology of the surface of the copper film (reduce irregularity of the surface) and prevent a void from being formed in a copper line. From the above-mentioned facts, it is an important object to perform the CVD under an atmosphere containing water vapor without causing problems such as reduction in adhesiveness due to formation of the oxide layer.    Patent Document 1: Japanese Laid-open Application No. 2002-60942: paragraphs [0037] and [0038] on page 5, and paragraph [0057] on page 6